New subject: [PATCH AUTOSEL 6.4 2/7] cifs: fix session state transition to avoid use-after-free issue

3 Aug 2023

From: Boris Brezillon boris.brezillon@collabora.com
[ Upstream commit e30cb0599799aac099209e3b045379613c80730e ]
drm_sched_entity_kill_jobs_cb() logic is omitting the last fence popped
from the dependency array that was waited upon before
drm_sched_entity_kill() was called (drm_sched_entity::dependency field),
so we're basically waiting for all dependencies except one.
In theory, this wait shouldn't be needed because resources should have
their users registered to the dma_resv object, thus guaranteeing that
future jobs wanting to access these resources wait on all the previous
users (depending on the access type, of course). But we want to keep
these explicit waits in the kill entity path just in case.
Let's make sure we keep all dependencies in the array in
drm_sched_job_dependency(), so we can iterate over the array and wait
in drm_sched_entity_kill_jobs_cb().
We also make sure we wait on drm_sched_fence::finished if we were
originally asked to wait on drm_sched_fence::scheduled. In that case,
we assume the intent was to delegate the wait to the firmware/GPU or
rely on the pipelining done at the entity/scheduler level, but when
killing jobs, we really want to wait for completion not just scheduling.
v2:
- Don't evict deps in drm_sched_job_dependency()
v3:
- Always wait for drm_sched_fence::finished fences in
  drm_sched_entity_kill_jobs_cb() when we see a sched_fence
v4:
- Fix commit message
- Fix a use-after-free bug
v5:
- Flag deps on which we should only wait for the scheduled event
  at insertion time
v6:
- Back to v4 implementation
- Add Christian's R-b
Cc: Frank Binns frank.binns@imgtec.com
Cc: Sarah Walker sarah.walker@imgtec.com
Cc: Donald Robson donald.robson@imgtec.com
Cc: Luben Tuikov luben.tuikov@amd.com
Cc: David Airlie airlied@gmail.com
Cc: Daniel Vetter daniel@ffwll.ch
Cc: Sumit Semwal sumit.semwal@linaro.org
Cc: "Christian König" christian.koenig@amd.com
Signed-off-by: Boris Brezillon boris.brezillon@collabora.com
Suggested-by: "Christian König" christian.koenig@amd.com
Reviewed-by: "Christian König" christian.koenig@amd.com
Acked-by: Luben Tuikov luben.tuikov@amd.com
Link: https://patchwork.freedesktop.org/patch/msgid/20230619071921.3465992-1-boris...
Signed-off-by: Sasha Levin sashal@kernel.org
---
 drivers/gpu/drm/scheduler/sched_entity.c | 41 +++++++++++++++++++-----
 1 file changed, 33 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index e0a8890a62e23..42021d1f7e016 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -155,16 +155,32 @@ static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
 {
    struct drm_sched_job *job = container_of(cb, struct drm_sched_job,
    					 finish_cb);
-	int r;
+	unsigned long index;
dma_fence_put(f);
/* Wait for all dependencies to avoid data corruptions */
-	while (!xa_empty(&job->dependencies)) {
-		f = xa_erase(&job->dependencies, job->last_dependency++);
-		r = dma_fence_add_callback(f, &job->finish_cb,
-					   drm_sched_entity_kill_jobs_cb);
-		if (!r)
+	xa_for_each(&job->dependencies, index, f) {
+		struct drm_sched_fence *s_fence = to_drm_sched_fence(f);
+
+		if (s_fence && f == &s_fence->scheduled) {
+			/* The dependencies array had a reference on the scheduled
+			 * fence, and the finished fence refcount might have
+			 * dropped to zero. Use dma_fence_get_rcu() so we get
+			 * a NULL fence in that case.
+			 */
+			f = dma_fence_get_rcu(&s_fence->finished);
+
+			/* Now that we have a reference on the finished fence,
+			 * we can release the reference the dependencies array
+			 * had on the scheduled fence.
+			 */
+			dma_fence_put(&s_fence->scheduled);
+		}
+
+		xa_erase(&job->dependencies, index);
+		if (f && !dma_fence_add_callback(f, &job->finish_cb,
+						 drm_sched_entity_kill_jobs_cb))
    		return;
dma_fence_put(f);
@@ -394,8 +410,17 @@ static struct dma_fence *
 drm_sched_job_dependency(struct drm_sched_job *job,
    		 struct drm_sched_entity *entity)
 {
-	if (!xa_empty(&job->dependencies))
-		return xa_erase(&job->dependencies, job->last_dependency++);
+	struct dma_fence *f;
+
+	/* We keep the fence around, so we can iterate over all dependencies
+	 * in drm_sched_entity_kill_jobs_cb() to ensure all deps are signaled
+	 * before killing the job.
+	 */
+	f = xa_load(&job->dependencies, job->last_dependency);
+	if (f) {
+		job->last_dependency++;
+		return dma_fence_get(f);
+	}
if (job->sched->ops->prepare_job)
    	return job->sched->ops->prepare_job(job, entity);
-- 
2.40.1


    

[PATCH AUTOSEL 6.4 1/7] drm/sched: Make sure we wait for all dependencies in kill_jobs_cb()